In drilling a well, a drilling tool or “drill bit” is rotated under an axial load within a bore hole. The drill bit is attached to the bottom of a string of threadably connected tubulars or “drill pipe” located in the bore hole. The drill pipe is rotated at the surface of the well by an applied torque which is transferred by the drill pipe to the drill bit. As the bore hole is drilled, the hole bored by the drill bit is substantially greater than the diameter of the drill pipe. To assist in lubricating the drill bit, drilling fluid or gas is pumped down the drill pipe. The fluid jets out of the drill bit, flowing back up to the surface through the annulus between the wall of the bore hole and the drill pipe.
Conventional oilfield drilling typically uses hydrostatic pressure generated by the density of the drilling fluid or mud in the wellbore in addition to the pressure developed by pumping of the fluid to the borehole. However, some fluid reservoirs are considered economically undrillable with these conventional techniques. New and improved techniques, such as underbalanced drilling and managed pressure drilling, have been used successfully throughout the world. Managed pressure drilling is an adaptive drilling process used to more precisely control the annular pressure profile throughout the wellbore. The annular pressure profile is controlled in such a way that the well is either balanced at all times, or nearly balanced with low change in pressure. Underbalanced drilling is drilling with the hydrostatic head of the drilling fluid intentionally designed to be lower than the pressure of the formations being drilled. The hydrostatic head of the fluid may naturally be less than the formation pressure, or it can be induced.
Rotating diverter heads provide a means of sealing off the annulus around the drill pipe as the drill pipe rotates and translates axially down the well while including a side outlet through which the return drilling fluid is diverted. Such rotating diverter heads may also be referred to as rotating blow out preventers or drilling heads. These units generally comprise a stationary housing or bowl including a side outlet for connection to a fluid return line and an inlet flange for locating the unit on a blowout preventer or other drilling stack at the surface of the well bore. Within the bowl, opposite the inlet flange, is arranged a rotatable assembly such as anti-friction bearings which allow the drill pipe, located through the head, to rotate and slide. The assembly includes a seal onto the drill pipe which is typically made from rubber, polyurethane or other suitable elastomer.
Rotating diverter heads have usually been made from a single piece casting and in some cases with welded construction. This usually includes the side outlet flange as well as the inlet flange on the bottom as an integral part of the assembly. This type of design carries with it some penalties for operability, maintenance and also lifespan of the assembly. In terms of operability the fixed design of the lower inlet flange needs a crossover if the connection on the Annular BOP (Blow out Preventer) is of a different size or pressure rating, which increase the vertical height of the assembly which limits the usability. Prior art rotatable diverter heads such as those disclosed in U.S. Pat. No. 8,286,734 have tried to address this stack-up height issue. There are also issues in terms of horizontal angular orientation with prior art designs which both U.S. Pat. Nos. 8,286,734 and 7,308,954 have addressed with different solutions. Some of the solutions proposed in U.S. Pat. No. 8,286,734 suggest a non API (American Petroleum Institute) connection to the Annular BOP. Many customers have issues with such non-standard connectors when it is directly interfacing with their equipment.
All prior art designs have the side outlet as a single fixed size and pressure rating design which sometime also require crossovers and these can be problematic in terms of the additional lever arm they produce on the assembly when valves and piping are added to this flange.
In terms of usability, the current design principles result in different housings to accommodate different inlet/outlet sizes and pressure ratings, with sometimes as many as 4 housings required to accommodate the different client requirements. Furthermore when “washout” (erosional damage) occurs on the side outlet, often the whole housing has to be junked.
There exists the need for a single central master housing that can be easily adapted for a range of inlet/outlet sizes and pressure ratings, which can accommodate horizontal angular rotation when required. This central master housing design will also preserve the long term integrity of the newly developed rotating head system as will be described below.